The invention relates to a continuously operating centrifugal separator drum for the concentration of suspended solids, in which the separated solids are delivered from the periphery of the drum through tubes or passages provided with nozzle-like orifice pieces, into a paring chamber located on a smaller diameter, and the concentrate is removed under pressure by means of a paring member.
Such centrifugal separators are known, and they are used for the purpose of achieving constant concentrations of solids from a varying input of solids. This is brought about, for example, by the mechanical or hydraulic operation of valves in the drum or by the displacement of paring members.
German Offenlegungsschrift No. 2,701,624 discloses such a centrifugal separator for the concentration of suspensions, the nozzle-like orifice pieces consisting of resilient, deformable tubular membranes communicating with the paring disk chamber, and the outlet cross section of the tubular membranes being variable under the action of the liquid pressure prevailing in the paring chamber, it being possible in this manner to regulate the concentration of the solids being removed.
In the case of certain solids having an abrasive character, such tubular membranes, however, are not so suitable since they are subject to rapid wear.
Also, French Pat. No. 1,554,226 discloses a centrifugal separator in which the operation of the outlet valves is accomplished in relation to the concentration of the solids by means of a hydraulically, pneumatically or electromagnetically operating closing means which is disposed in the hollow spindle of the centrifuge and opens the outlet aperture of the outlet valves as the concentration increases and closes it as the concentration decreases.
In this system, fine regulation of the valve and hence of the concentrate is not possible, since the valves can only be fully opened or fully closed. Furthermore, on account of the high pressures, forces and rates of flow in the drum, trouble is often encountered in these complicated designs, and the familiar ruggedness of nozzle-type centrifugal separators is lost.
In order to achieve a high concentration of the solids even when the input of solids varies, a portion of the removed concentrate can be delivered back into the drum ahead of the nozzles.
In this method it is furthermore possible to make the nozzle outlet cross sections larger, thereby better preventing clogging of the nozzles.
Such a method and apparatus are known, for example, from German Offenlegungsschrift No. 1,432,763. It is disadvantageous in this method, however, that the solid that has collected in the outer drum chamber is stirred up by the continuous feed of concentrate thus adversely affecting the outflow of the clear phase.